The present invention relates to an improved downhole bearing assembly for use with downhole motors and the like in drilling devices, in which the bearing assembly is effectively sealed against contamination.
It has been recognized for some time that downhole drilling motors can provide significant increases in drilling rates in many rock formations. However, in the past the use of downhole motors has often been limited by the life of bearing assemblies used in connection with such motors. These bearing assemblies typically include both radial and thrust bearings, and they operate under extremely adverse conditions.
In particular, downhole bearing assemblies typically operate in an environment dominated by high pressurized, highly abrasive drilling mud. Unless downhole bearing assemblies are properly designed, such abrasive drilling mud can severely limit the life of the bearing assembly, and thereby the utility of the downhole motor.
In the past, at least three approaches have been used in attempting to provide downhole bearing assemblies having an adequate bearing life. U.S. Pat. No. 4,320,929 discloses a sealed bearing system for hydraulically operated devices which attempts to seal out drilling mud and the like in order to protect the bearing assembly from abrasive contamination.
Another approach taken by the prior art is disclosed in U.S. Pat. No. 3,112,801, which describes a bearing assembly which is designed to operate with drilling mud as a lubricant. With this approach, sealing requirements are essentially eliminated.
A third approach is disclosed in Berryman U.S. Pat. No. 3,840,080, in which a sealed bearing system is filled with lubricating oil which is maintained at a higher pressure than the pressure externally of the section in order to retain the oil or other lubricant in a clean state. In particular, the Berryman system utilizes a sliding piston which is exposed to pressurized drilling mud and transmits pressurizing forces from the drilling mud to the lubricating oil.
In spite of the high level of activity in this field, a need presently exists for an improved, sealed downhole bearing assembly which can effectively protect bearings from abrasive drilling mud and provide an adequate bearing life.